In the present bending machines that are disposed generally horizontally, at least three rollers are rotatable together with respective supporting shafts having vertically arranged parallel axis. The vertical axis rollers co-operate in bending an elongated workpiece, such as a section or a pipe.
In these kinds of machines, the vertical axis rollers are arranged horizontally coplanar so that a workpiece helix extends in height in a cylindrical shape thanks to a horizontal axis roller being idly mounted downstream of the vertical axis third roller. Since the horizontal axis roller is height adjustably mounted so to project with respect to the vertical axis rollers, a helix pitch is obtained.
The diverging action exerted by the horizontal axis roller counteracting the action accomplished by the vertical axis rollers that would tend to maintain the elongated workpiece on the same plane of symmetry, determines a state of stress which irregularly deforms the elongated workpiece besides to wear unevenly the vertical axis rollers due to their eccentric operation.
The Chinese patent CN 2476361 describes a helical bending machine with multiple heads. In the patent drawings, bending rollers in one piece with internal helical wheels, are shown coplanar inclined according to the helix pitch of a pipe being worked with respect to respective drive shafts that the helical wheels engage by their internal toothings. However, it is not clear from the drawings how this inclined arrangement of assemblies of helical wheels and bending rollers is achieved and maintained, nor said arrangement is explained in detail in the description of the patent. If this inclined arrangement is achieved by an inclination of the internal helical wheels with respect to the rollers that are external to them, this inclination should be able to be changed depending on the helix pitch of the workpiece, or the assemblies of helical wheels and bending rollers should be changed every time a helical bending operation is decided to be performed with a different pitch.
Furthermore, since the bending machine in the above mentioned Chinese patent is not of the kind in which the bending rollers are integral with the supporting shafts like in the bending machine of the present invention, but they are moved by shafts through respective toothings, the construction of the bending machine is particularly complex and susceptible to failure and breakdown.